Discontinuous Reception (DRX) and Discontinuous Transmission (DTX) were introduced in the CELL_DCH state as part of the Continuous Packet Connectivity (CPC) feature of the Third Generation Partnership Project (3GPP) Release 7. DRX and DTX operation, applied to wireless transmit/receive units (WTRUs) in the CELL_DCH state, allow the radio access network to maintain temporarily inactive WTRUs in the CELL_DCH state by reducing the interference cause by these WTRUs (i.e. reduce wasted system capacity) and reducing the WTRU battery consumption.
In Release 7, a two-tiered DRX scheme was introduced for WTRUs in the CEL L_PCH state. Upon transition to the CELL_PCH state the WTRU enters DRX mode using a shorter DRX cycle and after a period of inactivity the WTRU switches to a longer DRX cycle.
A new feature has been introduced as part of 3GPP Wideband Code Division Multiple Access (WCDMA) Release 8 to enable DRX operation for a WTRU in the CELL_FACH state. A fixed DRX pattern was introduced which is in constant use during the entire time period that a WTRU is in the CELL_FACH state with the exception of when the WTRU has enhanced Dedicated Channel (E-DCH) resources allocated. When the WTRU is allocated E-DCH resources it may operate in continuous reception and transmission mode, allowing it to continuously transmit and receive continuously on the downlink. After the E-DCH resources are released, the WTRU and a Node-B then start to follow the fixed DRX pattern derived from a Radio Network Temporary Identifier (RNTI) of the WTRU.
The DRX pattern used by a specific WTRU may be determined by a user-specific identifier such as an E-DCH-RNTI (E-RNTI), High-Speed Downlink Shared Channel (HS-DSCH) RNTI (H-RNTI), or Controlling Radio Network Controller (C-RNTI). The behavior of the WTRU and the DRX pattern is not specified for a WTRU that does not have an allocated RNTI (e.g. when the WTRU sends a CELL_UPDATE for cell reselection and has not yet received its CELL_UPDATE CONFIRM message). Additionally, WTRU behavior is not defined for when a radio link failure occurs in the CELL_DCH state. A WTRU experiencing the radio link failure moves to the CELL_FACH state and deletes all the dedicated downlink and uplink information allocated to the WTRU while in CELL_DCH. These resources include the E-RNTI, H-RNTI, and C-RNTI. The WTRU then sends a CELL UPDATE message with cause “radio link failure” and waits for the CELL UPDATE CONFIRM. During this time, the WTRU does not have a dedicated RNTI. Further, no DRX behavior is defined for a WTRU in idle mode and initiating a Radio Resource Control (RRC) connection request. When a WTRU is in idle mode, the WTRU may not have a dedicated RNTI when a RRC Connection Request message is sent. As a result, the WTRU has to wait to receive a RRC Connection SETUP message from the network over HS-DSCH, which may assign a dedicated RNTI to the WTRU.
Similarly, methods for managing the transitions of a WTRU between DRX operation and Continuous Reception (CRX) operation are desired. In one proposal a WTRU may be configured to link the transition between DRX operation and CRX operation to the start of an enhanced random access channel (E-RACH) access or an E-DCH in the CELL_FACH state and Idle mode procedure. Further, the transition of a WTRU between CRX operation to DRX operation may be linked to the release of its allocated E-DCH resources. However, this behavior may create problems because a WTRU may be operating in DRX in certain conditions where it would need to be listening for signaling or data from a UMTS Terrestrial Radio Access Network (UTRAN). For example, such a scenario may occur when a WTRU sends a CELL_UPDATE message for cell reselection using the E-DCH in the CELL_FACH state to move to a new Node-B and then resumes DRX operation after releasing its E-DCH resources. If the new Node-B is unaware of the DRX pattern used by the WTRU, it may transmit its response (e.g. the CELL_UPDATE CONFIRM) while the WTRU is in DRX, thus preventing the WTRU from receiving the response. Another scenario where a problem may occur is when a WTRU sends a CELL_UPDATE message for cell reselection using the Random Access Channel (RACH) to moves to a new Node-B. Since the start of a RACH access procedure is not currently a trigger to transition from DRX to CRX, the new Node-B may transmit its response (e.g. the CELL_UPDATE CONFIRM) while the WTRU is in DRX, thus preventing the WTRU from receiving the response.
Another problem may occur if the WTRU is allowed to autonomously release the E-DCH resources and the network does not receive an indication that the resources were released. In this scenario, the WTRU may be in DRX operation while the network thinks the WTRU is still in CRX mode because the E-DCH resources are still allocated. This may result in the WTRU failing to receive a message in the downlink.